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Ryan Singh, Jiri Herza, James Thorp, Michael Ashley
Performance-based risk-informed decision making is an underlying principle of the Global Industry
Standard on Tailings Management (GISTM). While owners make significant efforts to align with this
principle, commonly used risk assessment and management practices in the mining industry have largely been based on the HSE principles, which consider more frequent, lower consequence incidents.
As a result, the existing risk assessment frameworks do not provide the owners with a comprehensive understanding of the risk profiles of their tailings storage facilities (TSFs). Without the understanding of a facility’s risk profile, the owners cannot appreciate how changes to their facility, processes and operational activities may impact the risk profile. A large step-change in thinking is therefore required in risk assessment practices for the owner to align their TSF management with GISTM requirements.
Beyond risk assessments, the mining industry has other valuable concepts to manage the safety of their tailings management practices, such as Critical Controls, however, commonly used risk assessment and management practices do not incorporate these concepts.
This paper explores commonly used risk assessment practices and the concepts of Critical Controls. It proposes how these concepts can be linked, with Critical Controls being embedded in the risk assessment process. The outcomes of linking these concepts result in an estimation of the effectiveness of the Critical Controls and how they can be improved to demonstrably reduce the risk presented by a TSF. A case study has been included to demonstrate the benefits of linking risk assessment with Critical Controls and how owners can readily identify deficiencies and efficiently manage the risk profiles of their facilities.
Now showing 25–36 of 55 search results:
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2021 Papers
2021 – The Critical Link between Risk Assessments and Critical Controls
Learn moreRyan Singh, Jiri Herza, James Thorp, Michael Ashley
Performance-based risk-informed decision making is an underlying principle of the Global Industry
Standard on Tailings Management (GISTM). While owners make significant efforts to align with this
principle, commonly used risk assessment and management practices in the mining industry have largely been based on the HSE principles, which consider more frequent, lower consequence incidents.As a result, the existing risk assessment frameworks do not provide the owners with a comprehensive understanding of the risk profiles of their tailings storage facilities (TSFs). Without the understanding of a facility’s risk profile, the owners cannot appreciate how changes to their facility, processes and operational activities may impact the risk profile. A large step-change in thinking is therefore required in risk assessment practices for the owner to align their TSF management with GISTM requirements.
Beyond risk assessments, the mining industry has other valuable concepts to manage the safety of their tailings management practices, such as Critical Controls, however, commonly used risk assessment and management practices do not incorporate these concepts.
This paper explores commonly used risk assessment practices and the concepts of Critical Controls. It proposes how these concepts can be linked, with Critical Controls being embedded in the risk assessment process. The outcomes of linking these concepts result in an estimation of the effectiveness of the Critical Controls and how they can be improved to demonstrably reduce the risk presented by a TSF. A case study has been included to demonstrate the benefits of linking risk assessment with Critical Controls and how owners can readily identify deficiencies and efficiently manage the risk profiles of their facilities.
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Guidelines
ANCOLD Guidelines on Risk Assessment (July 2022)
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Please note only available in hardcopy format.The ANCOLD Guidelines on Risk Assessment were published in 2003. They have served the Australian dam community very well and are referenced internationally. Risk assessment is now the principal approach to manage engineering risks at water dams and now a developing practice for tailings dams.
These new guidelines on risk assessment replace the 2003 publication. They include updates to several sections taking account of developments in risk analysis methods and risk evaluation, from experience in applying those guidelines. As for ANCOLD (2003), these guidelines are directed to the practical application of risk assessment, as an aid to better dam safety management. Risk management is the end objective – risk assessment is a means to that end.
These guidelines have been produced by a Working Group of six members, all with significant experience with risk assessments for dams. A Reference Committee of sixteen members has been engaged throughout the development of the Guidelines.
The Working Group and Reference Committee include representatives of dam owners, consultants, universities, and regulators of dam safety. Six Australian states and the ACT were represented. Members and associates of ANCOLD have also provided input through risk workshops held with annual conferences.
Dam owners, decision-makers and analysts need to consider the current state of development of risk assessment in deciding how best to use and apply the process in reaching decisions on dam safety, having regard to their specific overall business risk management needs, and their community and legal responsibilities.
These guidelines also require consideration by dam safety regulators, who need to decide what part risk assessment can play in the discharge of their responsibilities. Deciding on the tolerability of risk is one of the functions of regulators.
ANCOLD continues to believe that the use and further development of risk assessment using studies of the traditional engineering standards-based approach as an input, as proposed in these guidelines, offers the potential for significantly improved dam safety management.
Risk assessment methods are continuously developing. ANCOLD recognizes that detailed aspects of these guidelines will be overtaken by developments within a few years and urges practitioners to keep abreast of new knowledge. Nevertheless, the framework and generic guidelines in this publication are essentially as detailed in ANCOLD (2003) and are expected to remain valid for many years.
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2014 Papers
2014 – Is it Safe Enough? The Dam Safety Case
Learn moreShane McGrath, Phillip Cummins, and David Stewart
Dam owners and regulators now commonly use risk assessment techniques to assist with decision making for an individual dam or a portfolio of dams. In many cases risk assessment is used to select an optimal course of action in relation to ongoing safety performance of dams, including the achievement of public safety objectives. However, whilst it is an important tool, the use of risk assessment alone is not sufficient to establish that a dam is “safe”.
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In modern organisations, business objectives are achieved through a systematic approach to management which described simply sets out what needs to be achieved, how the required outcomes will be delivered and audits the process and results.
In hazardous industries such as mining, chemical, nuclear and dams, it is necessary to reliably achieve business objectives such as product volumes, unit costs and workplace health and safety alongside public safety objectives. In the dams industry, dam safety management systems are now being implemented to document how the organisation satisfies its corporate and business objectives, governance responsibilities and risk management processes.
It is also common in hazardous industries that a “safety case” is required by regulators to demonstrate that the owner has identified what could go wrong at its facility, what controls are in place and that there is a system in place to ensure that the controls are reliable. Whilst dam owners may rely on a dam safety risk assessment to meet regulatory obligations and demonstrate due diligence, the results of risk assessments are not routinely documented sufficiently to satisfy a “safety case” and therefore will not fully meet the organisation’s requirements.
Many dam owners are also responsible for the safety management of other hazardous facilities, such as urban water and mining corporations which typically manage hazardous chemical installations and hazardous or toxic waste disposal. For such organisations, the corporate awareness and processes should already exist to extend the “safety case” philosophy to the management of their dams.
This paper sets out the importance of a dam “safety case”, the essential elements of a safety case and its relationship to the dam safety management system. -
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2013 Papers
2013 – Development and application of a risk based approach to managing floods during construction
Learn moreSimon Lang, David Stephens, Peter Hill, Mark Arnold and Tommie Conway
Considerable thought has been given in recent years to managing the risks associated with floods during the construction of new dams and dam upgrades. Both ANCOLD and the NSW DSC provide some limited advice on how this risk should be managed, with many dam owners aiming for societal risk during construction to be no higher than pre-construction. One approach to do this is to draw down the reservoir such that sufficient airspace is created to reduce the probability of overtopping the construction works to be equal to that of overtopping the dam crest pre-construction. However, this frequently leads to very large releases of valuable water resource being required. This approach also fails to consider that the conditional probabilities of failure may be quite different during construction than during normal operation. A risk-based approach was applied for the recent upgrade of Tarago Reservoir. Existing event trees from a failure modes analysis were adjusted to reflect the construction conditions. In some cases, the event probabilities increased (for example as a result of excavation of the dam embankment), however some also decreased (for example as a result of more rapid means of detecting and intervening in breach formation during construction). The conditional probabilities of failure during construction were then used to estimate the overall seasonal probability of failure, and it was found that a limited draw down of the reservoir would be sufficient to ensure that risks were no higher during construction than pre-construction. To reinforce this, the cost-to-save-a-statistical life was estimated for further drawdown of the reservoir and used to demonstrate that the risks were as low as reasonably practicable.
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2013 Papers
2013 – Case study of risk assessment for dam safety management decision-making in Korea
Learn moreJeong Yeul, Lim
For various historical reasons and some technical reasons, the safety of dams has been evaluated using an engineering standards-based approach, which was developed over many years. It was used initially for the design of new dams, but increasingly has been applied over the past few decades to assess the safety of existing dams. Some countries have carried out risk assessments of existing dams that included both the structural and hydraulic safety of the dam and social risk. These methods developed by other countries could be adapted to assist in decision-making for dam safety management. Unfortunately, methods for risk assessment of dams were not established in Korea. This study outlines a beginning risk analysis for structural safety management. The first stage consisted of research on the present domestic dam safety guidelines and reviewing operations for management systems of dam safety abroad. Also, dam risk analysis requires reliable data on dam failure, past construction history and management records of existing dams. A suitable risk analysis method of dams for structural safety management in Korea is use of event tree, fault tree and conditioning indexes methods. A pilot risk assessment was carried out for two dams. The dam risk assessment process was thus established, and we learned the importance of risk assessment. The future includes additional research and risk analysis to develop the system.
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2013 Papers
2013 – Flooded cars: estimating the consequences to itinerants exposed to dam break floods on roads
Learn moreJamie Campbell, Gregg Barker, Paul Southcott and Michael Wallis
The assessment of consequences of dambreak is used as input to the design parameters of dams, dam safety requirements and dam risk assessments. For many low consequence category dams, the consequences of failure can be dominated by itinerants, in particular vehicles on roads within the dambreak inundation area. Estimating the population at risk (PAR) and potential loss of life (PLL) rigorously is mathematically complex, requires significant user judgment and can be very sensitive to input assumptions. This paper presents a simple, practical tool that has been developed to assist engineers and analysts in assessing the PLL of itinerant road users within a dambreak inundation zone. The tool allows for a logical and defensible analysis based on an event tree approach and provides guidance on appropriate factors to be used in calculating the overall fatality rate of people exposed to the dambreak hazard. This paper details the tool and how to apply it to typical dambreak problems, providing the reader with the information required to estimate the consequences on itinerant road users; the paper also details how the concepts discussed can be applied to other itinerants.
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2013 Papers
2013 – A case study: how to minimise risks associated with a portfolio of non-revenue generating dams
Learn moreMonique de Moel and Gamini Adikari
Parks Victoria manages over 4 million hectares of parkland and a portfolio of over $1.9 billion worth of infrastructure assets. Within this portfolio, Parks Victoria is responsible for a large number of dams and their associated structures. Consequence category of these dams varies from Extreme to Very Low. Parks Victoria recognised that these assets required a dam safety management and monitoring program. The development of a program commenced with a portfolio risk assessment in 1998 which progressed to detailed design reviews of a selected number of dams and the initiation of an ongoing dam safety and surveillance program. This initial work identified the need for dam safety upgrade works within this asset portfolio which Parks Victoria has been progressively addressing. In 2012 Parks Victoria identified that a review of the risk profile of the dams was warranted. The review included consideration of alternative options such as staging of works, reducing storage volume and decommissioning, as well as non-technical considerations such as increasing the recreational use and the environmental value of these assets. This paper outlines the approach adopted by Parks Victoria in developing and improving its dam safety program and how it has assisted in minimising dam safety risks. Specifically, Parks Victoria’s approach of adopting measures that recognize the purpose and benefits of the individual storages, whilst being sympathetic to the requirements of the other infrastructure within its diverse portfolio of assets is highlighted. Since this work commenced in 1998, Parks Victoria have been successful in the development of an effective dam safety and management program which has resulted in the reduction of risks associated with this portfolio of assets.
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2007 Papers
2007 – Seismic hazard assessment of the Lake Edgar Fault
Learn moreA. Swindon, M. Gillon, D. Clark, P Somerville, R. Van Dissen and D. Rhoades
The 45 km long Lake Edgar Fault in south-west Tasmania passes through the right abutment of the Edgar Dam and into Lake Pedder, and within 30 km of three other large dams. In 2004 an independent seismotectonic study concluded that the fault had moved three times in the past 48–61,000 years, with the last movement around 18,000 years ago.
In order to better constrain the risk assessment for the nearby dams, the likelihood of a rupture recurrence along the fault was required. Two independent methods were investigated. The first was a comprehensive review of active faulting and deformation of stable continental region faults within Australia, and a comparison with similar faults worldwide with the well studied behaviour of the Lake Edgar Fault. The study results demonstrated the episodic nature of stable continental region fault activity, separated by much longer periods of quiescence, with a decreasing likelihood of rupture following each event within an active period. The time window of applicability of this paleoseismological study is thousands to tens of thousands of years.
The second study looked for evidence of precursory seismic activity in the vicinity of the fault which could indicate an increasing risk of rupture over the next decade or so. This method does not predict specific earthquakes, but does forecast whether the level of future earthquake activity in the short to intermediate term is relatively low, high or at an average level. Using a catalogue of seismic activity for south-eastern Australia, the study concluded that there is no evidence for precursory seismic activity in the area of the Lake Edgar Fault that would give rise to an elevated forecast rate of occurrence of moderate magnitude earthquakes either in the short to intermediate term. This precursory method has a window of applicability of a decade to perhaps several decades.
The combination of these two studies has advanced the understanding of the Lake Edgar Fault activity by both setting it in the long-term stable continental region fault context and investigating the presence of short-term behavioural activity. This has allowed the seismic hazard to be re-assessed as nearer to ambient levels than earlier postulated. This work has applicability for other fault scarps in Australia, both with regards to better defining the long-term hazard (103-105 years) posed by a fault, and potentially also giving advance (short-term 101 years) notification of increasing risk of fault rupture. Better long- and short-term hazard information allows more complete and thorough engineering decisions to be made.
Keywords: Earthquake, seismic, fault rupture, dam safety, risk assessment, Hydro Tasmania, Lake Edgar Fault.
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2012 Papers
2012 – Risk assessment for managing impacts of mining on dams
Learn moreDavid Hilyard, William Ziegler, Heather Middleton
New South Wales has a significant number of dams, including major water supply dams, located over or near mines. Mining near dams imposes dam safety risks including: mine subsidence, mine blast vibration, presence of mine personnel downstream, rapid changes in consequence during mining, and loss of stored waters. The NSW Dams Safety Committee(DSC) regulates mining near dams, using risk assessment to review applications to mine near dams. A structured approach allows rational, evidence-based decision making by stepping through a procedure involving: initial consultations, screening risk assessment, evaluation of technical arguments, risk assessment, and development of risk management strategies. The risk assessment for dam walls develops acceptance criteria, reviews 19 possible risks to dam walls, and site-specific hazards. For potential for loss of stored waters, four possible groups of flow paths from storage to underground mine are reviewed; flows are evaluated with Monte Carlo simulation in terms of tolerable loss. Risks are assessed from a dam engineering viewpoint, which may be more conservative than the perception of risk in the mining industry, considering both tolerable risks and operational time frames. Case studies include: a tailings dam 100 m upstream of an active open cut and underground portal was undermined by longwall mining, with about 1.5 m subsidence of parts of the embankment as each of four longwall panels was extracted; longwall mining beneath a major Sydney water reservoir, with no observed impact on the stored waters; and open cut mining immediately downstream of a mine water dam. Risk-based methodology has provided the DSC with increased confidence in reviewing applications to mine near dams.
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Keywords: Mining, dams, risk assessment, New South Wales, Dam Safety Committee -
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2012 Papers
2012 – Oberon Dam – Failure hazard of a buttress dam and its vulnerability to earthquake damage
Learn moreChi-fai Wan, Jason Hascall, Andrew Richardson, John Sukkar
Oberon Dam is the major headwork of the Fish River Water Supply Scheme providing bulk water supply to Oberon Shire and Lithgow City Councils, Sydney Catchment Authority, and Delta Electricity. The dam is owned and operated by State Water Corporation (SWC).
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Located on the Fish River 2km south of Oberon in New South Wales, Oberon Dam was completed in two stages in 1946 and 1957. In 1996 the dam was upgraded to pass the 1993 Probable Maximum Flood estimate by raising the dam 1.77m and constructing a 50m wide auxiliary spillway on the left abutment. The upgraded dam comprises a 232m long, 35.3m high concrete slab and buttress section and a 165m long earth embankment section.
A typical buttress dam has its inclined upstream face made up of relatively thin reinforced concrete slabs supported by but not integral with the buttresses, making a relatively flexible dam structure vulnerable to earthquake damage.
As buttress dams evolved from concrete gravity dams, their structural design follows the same principles as applied to gravity dams. However, many buttress dams were designed over 60 years ago using outdated methods that did not consider earthquake loads. Current overseas and local design guidelines do not provide sufficient guidance for checking the seismic stability of existing buttress dams. For instance, the simplified seismic analysis, proposed by Fenves and Chopra to investigate the seismic response of gravity dams to earthquake loads in the upstream-downstream direction, is not applicable to buttress dams which are also susceptible to damage by earthquake loads in the cross-valley direction.
SWC engaged Black & Veatch to carry out a three-dimensional finite element analysis of Oberon Dam to better understand the structural behaviour of the dam under earthquakes. The analysis used both the response spectrum and time history approaches. Due to the uncommon design of Oberon Dam and the limited discussion found in the literature on the dynamic behaviour of buttress dams, the Authors would like to share their experience in the assessment of the hazard, and on the use of modern finite element modelling techniques to investigate the dynamic response of this type of dam.
Keywords: Ambursen dams, Buttress dams, Risk assessment, Time history analysis, Finite element -
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2012 Papers
2012 – Baseline Risk Assessment for Herbert Hoover Dike
Learn moreDavid S. Bowles, Sanjay S. Chauhan, Loren R. Anderson, Ryan C. Grove
A risk assessment (RA) was conducted for 27 miles of Herbert Hoover Dike to better understand and estimate the Baseline failure risk. Unique aspects of this risk assessment included the following: high stillwater levels persisting for almost a year; highly dynamic and spatially variable wind loading; short-duration wind setup that reduces likelihood of piping; dike length that increases probability of failure; and multiple breaches with overlapping inundation areas that affect failure probability and consequences and the risk evaluations.
A wide range of stillwater and wind loading combinations were considered. Following a potential failure modes analysis (PFMA), failure modes included were: piping through foundation, embankment piping, piping along conduits, piping along structures through embankment, embankment and flood wall instability, and overwash and overtopping. System response probabilities (SRPs) were estimated using toolboxes, analyses and expert judgment. Life-loss consequences were estimated using LIFESim. RA calculations were performed using DAMRAE-HHD, which includes length effects. Estimated risks were evaluated against the US Army Corps of Engineers (USACE) tolerable risk guidelines (TRG). Uncertainties were explored using sensitivity analyses.
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2008 Papers
2008 – Proposed changes to the UK Reservoir Safety Legislation to incorporate a risk based approach and the problems the UK faces into future
Learn moreDr AK Hughes
Abstract: This paper describes the way in which the UK is moving in respect of reservoir safety and outlines the legislative changes that are currently being drafted. It also identifies issues which the author thinks are important for the future of dam engineers around the world.
Keywords: safety, legislation, risk assessment
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2008 Papers
2008 – Risk assessment in spillway remedial works design and construction and monitoring at Googong Dam
Learn moreJames Willey, Malcolm Barker, Javad Tabatabaei
Abstract: During successive flood events from the end of construction of Googong Dam in 1978 through to the late 1980s, erosion of in excess of 5,000 m³ of rock occurred in the partially unlined section at the downstream end of the spillway channel. Remedial works were undertaken in stages during the 1980s to stabilise the eroded chute and limit further erosion. A project is currently underway as part of the Bulk Water Alliance to construct remedial works in the spillway to repair erosion damage and increase the spillway capacity to safely pass the current estimate of the Probable Maximum Flood. The design was undertaken by GHD Pty Ltd as part of a separate engagement prior to the formation of the Alliance.
The recent work involved a review of the historical performance and prediction of future performance of the structure. A process involving the development and comparison of options and ultimately the detailed design of the preferred arrangement followed, including refinement and validation using a physical hydraulic model study.
This paper presents risk assessment techniques used throughout the project on a range of tasks including prediction of future spillway erosion damage and comparison of spillway remedial works options, assessment of construction flood risk and definition of instrumentation requirements for the dam and associated structures.
Keywords: risk assessment, remedial works, spillway erosion, rock erosion, construction risk, instrumentation.
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2008 Papers
2008 – Risk assessment with uncertainty analysis for an already-initiated failure mode
Learn moreDavid S Bowles, Sanjay S Chauhan, Loren R Anderson, Terry F Glover
Abstract: A nested model is presented for considering variability and knowledge uncertainty in a dam safety risk assessment of an existing dam and interim risk-reduction alternatives (operating restrictions) during the staged implementation of a permanent structural risk reduction measure. The effects of some important aspects of natural variabilities on estimated risks are represented as cumulative distributions of probability of failure, annualised life loss, economic risk cost, and an F-N representation of life loss. Many cumulative distributions are generated to represent the effects of some important aspects of knowledge uncertainties.
An important aspect of the knowledge uncertainty is the current level of development of an already-initiated piping failure mode. Also, an approach to conditioning the system response probabilities (SRPs) for the piping failure mode on the duration of reservoir pool exceedance is included in the failure event tree risk model.
ANCOLD and Reclamation tolerable risk guidelines are evaluated at selected percentiles of variability and percentiles (levels of confidence) of knowledge uncertainty. The incremental cost-per-statistical-life saved and benefit-cost ratio for interim risk-reduction alternatives are estimated and evaluated to examine the case for more-severe levels of operating restriction than the least-severe operating restriction that is estimated to satisfy, at a selected percentile of variability and a desired level of confidence, the limit values in all of the tolerable risk guidelines that were considered.
Keywords: Dam safety, risk analysis, risk assessment, uncertainty analysis, aleatory uncertainty, epistemic uncertainty.
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2008 Papers
2008 – An overview of risk assessment tools for US Army Corps of Engineers dams
Learn moreDavid M Schaaf, Jeffrey A Schaefer, Rick W Schultz, Jason T Needham
Abstract: As one of the main federal agencies with responsibility to build, operate, and maintain large dams in the United States, the US Army Corps of Engineers (USACE) is developing a risk based framework to better manage their portfolio of 600+ dams in terms of risk management and prioritization of funding. A key element to this effort is the development of risk-based analytical tools to evaluate primary features for applicable failure modes. These are used in conjunction with loading and consequence modules to assess the overall risk associated with the dam in terms of lives and economic damages. The focus of this paper is on the engineering analysis modules used to generate fragility curves for dam features.
The analysis modules are broken into three main categories by engineering discipline: geotechnical, structural, and mechanical/electrical. The risk based assessment tools associated with geotechnical failure modes include Seepage & Piping, Embankment Stability, Seismic Performance, and Erosion of Unlined Spillways. The structural assessment tools include Concrete Monolith Stability, Spillway Gates, Scour of Concrete Lined Spillways, Spillway Training Wall Stability, Performance of Pipes through Dams, Hydropower Superstructures and Intake Towers. The mechanical and electrical are primarily focused on the performance of machinery used to operate dam gates.
This paper gives a broad overview of the main characteristics and methods used for each of these analysis tools. Some of the modules use historical performance to establish failure rates, while others are more analytically based. The context of each within the framework of the overall risk assessment effort of USACE dams is covered.
Keywords: risk based analytical tools, fragility curves, risk assessment, US. Army Corps of Engineers, portfolio, dams.
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2009 Papers
2009 – Innovative Solution to foundation piping risk at Hinze Dam
Learn moreGavan Hunter, Chris Chamberlain, Mark Foster
Hinze dam, an extreme hazard storage, is under the authority of Seqwater (Southeast Queensland) and is principle potable water storage supplying the Gold Coast. Hinze Dam Stage 3, presently under construction, involves raising the existing embankment almost 15m to a maximum height of 80m.
The foundation geology on the right abutment of the main embankment comprises of a deeply weathered sequence of greywacke and variably silicified greenstone and chert. The deeply (and variably) weathered soil profile below the right abutment of the existing embankment presented an unacceptable piping risk for the embankment in its existing condition. Contributing factors included: 1/ the highly erodible extremely weathered greywacke and presence of continuous defects in the weathered soil mass; 2/ the extremely weathered greenstone in direct contact with highly fractured, highly permeable silicified greenstone and chert bodies aligned normal to the dam axis which provide continuous seepage paths through the foundation.
Works were required as part of the Stage 3 raise to address the foundation piping risk. Significant issues for design included: 1/ the depth of weathering extended up to 25to 40m into the foundation.; 2/ extremely weathered and highly erodible greenstone was present below the right abutment of the embankment and extended down to the lower abutment some 50 to 60 m below the existing dam crest; 3/ the reservoir level could not be drawn down during construction and the probability it would be near full supply level during the works was high; and 4/ the variability of strength in the greenstone form soil to extremely high strength presented challenges for excavation.
The options assessed to address the piping risk included a plastic concrete cut-off wall and an upstream blanketing option. The plastic concrete cut-off wall (220m long and up to 50m deep) and deep filter trench was the selected option. The cut-off wall had been successfully completed ahead of time and below budget. The innovative design required excavation through earthfill core of the embankment under full reservoir level and use of a purpose built trench cutter (by Bauer Foundations Australia) for the variable excavation conditions.
Keywords: dam safety, piping, risk assessment, cut-off wall.
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